I was going to build one, but when I tallied up the price, and it was almost as much or more than a factory built system. That quickly changed my mind. Then I saw an ad on specials for the 4th of July. It is from Global. They were offering a 64 bit, AMD chip, with a mother board that has all kinds of expansion capabilities. The power supply is 400 watts. It comes with a DVD + - R, RW double layer drive, a 120GB SATA hard drive, The sound and video is integrated, but can be shut off in favor of a board. Network is integrated. The support chips are NVIDIA. It comes with Win**XP Pro, and one gig of ram. There is a connector on the board for a couple of Floppy drives, and it supports parallel hd's as well as SATA drives. The case is roomy enough for expansion. The whole thing went for ONE GRAND, minus a penny. Shipping is free.The setup is about as close as what I was about to put together, and for a lot less money. I was initially going to order a bare bones system, but this changed my mind.I guess that I will add another hard drive to install 64 bit linux, and I should be well on my way to happy computing.

This thread hasn't been updated in a while. I think the economics have changed even more, and nowadays it makes sense to build your own if:

You have done so before, have a nice case and reusable parts and want to upgrade.

You are building a high end game machine and want to control all the inputs carefully.

You want to run Linux and not buy Windows as part of the package.

You want to have fun and learn something about computers by building one.

I went through this exercise recently when I got a new desktop to run Windows 7. I was able to buy a fairly nice business grade Acer i5 system and tweak it a bit to improve graphics for less than the parts would have cost me.

My No.1 is in a state of constant upgrade. While the case is about 7 years old, it has had 2 mobos, 3 graphics cards, 2 RAM upgrades, 3 power supplies and many drives. Still looks the same (except for the 3 different monitors).
Building your own is fun and rewarding.

registered Linux user number 324659 || The importance of Reading The *Fine* Manual! :D
For the things we have to learn before we can do them, we learn by doing them.

I think that historically, looking at the power user group, it has never been about 'money'. The computer hobbyists tend to do it more for enjoyment, choosing quality components etc. Having said that, when you consider the present market conditions, DIY makes sense only for the computer hobbyist these days. The cost of a desktop PC these days has become so low that it's much better for the average user to buy one rather than build.

My last build was a Shuttle XPC. I wried in switches in the back in order to allow me to turn the front panel LEDs off if I chose (Why people put lights and LEDs in their cases is beyond me). That little machine is chugging along almost constantly. The only repair I've needed to make is a replacement CMOS battery.

a friend builds the servers for his work, the case looks like what ibm is entombing their rack-mount servers in.
he builds to the same specs as a dell, hp or ibm, but claims he saves about 50% of the cost...

One of the joys of BIY is the neverending mods you can make. Yesterday I received my 10 port USB 2.0 thingy that fits into the old floppy spot in my tower. It's a marvel of engineering with not only 10 ports packed neatly in, but a nifty little power light too!
The real surprise is that it was free shipping and came from Hong Kong. Took 7 days. What's the deal with that? Half way around the world and only 7 days. So now I get to open my case and add a new toy and hopefully clear up some clutter.

A few things I learned over the last couple of years about new desktop systems:

You'll likely only need to replace the CPU box when you upgrade. The speakers and monitors last a long time and if you have DVI or HDMI on the monitor you are good to go.

If you buy, go for a business grade unit. You'll get a nicer case with better cable management and a decent mobo/CPU combination. My Acer Veriton even has an upgraded cooler for the CPU, and also features Windows 7 Pro. A lot less crapware as well.

That said a commercially available unit will have some compromises. In my instance it was a wimpy power supply and poor integrated video - fine for business but no good for gaming. I had to pay extra to replace the PS and add a video card. Cooling was also inadequate so I had to put in a case fan. I also added some RAM so at the end of the day it probably would have been cheaper to spec and build the machine as I now have it.

If you are going to get a new machine for Linux, there's no question that you should build it yourself. You can make sure your hardware is Linux friendly, and you don't have to buy Windows or remove it from the PC. You also don't have to worry about the UEFI/Secure Boot nonsense either if Windows 8 was never installed.

Bottom line - if you are upgrading a desktop system it still makes a lot of sense to DIY even if the economics are about the same.